This invention relates to a process for isomerizing the double bond in olefins to provide different, isomeric olefins.
This invention also relates to a novel catalyst composition useful as a catalyst for olefin double bond isomerization.
This invention further relates to a process for isomerizing the double bond of an olefin without undesirable polymerization or skeletal isomerization.
A number of catalysts capable of isomerizing the double bond of an olefin are known in the art. Such catalysts are capable, for example, of converting butene-1 to butene-2, the 2-isomer being more valuable commercially than the 1-isomer. Many of the previously known catalysts have been found deficient in various ways, especially where they are employed under commercial operating conditions.
One serious drawback found in many previously disclosed olefin isomerization catalysts is their lack of selectivity. In an olefin isomerization operation, the catalyst must be selective for the double bond shift. For example, when it is desired to convert butene-1 to butene-2 a more valuable chemical, the catalyst must be capable of selectively catalyzing this double bond shift without converting the butene-1 to other compounds such as polybutenes, isobutylene, n-butane, or lower molecular weight hydrocarbons. In this case, selectivity refers to the ability of the catalyst to isomerize the double bond in the reactant without causing the reactant compound to polymerize, crack or hydrogenate, or causing carbon chain rearrangement in the reactant compound.
In order for a double bond shift catalyst to be commercially acceptable, it must be active for the desired double bond shift at temperatures at which equilibrium between double bond isomers favors conversion to the desired double bond isomer, while remaining inert with respect to other compounds commingled with the reactant compound during the isomerization reaction. The olefins which it is desired to isomerize in commercial operations are generally available only in admixture with other hydrocarbons. For example, in all economically feasible sources of butene-1, it is available only in admixture with isobutylene. Because of the very similar boiling points of butene-1 and isobutylene, it is completely impractical to attempt to separate butene-1 from isobutylene by fractionation. Butene-2, on the other hand, can economically be separated from butene-1 and isobutylene by fractionation. Thus, in commercial operation for isomerizing butene-1 to provide butene-2, the butene-1 feed to the isomerization operation always contains a significant amount of isobutylene. In order to utilize an olefin isomerization catalyst in such an isomerization operation, the catalyst must be capable of catalyzing the conversion of butene-1 into butene-2 at temperatures where butene-2 is favored by equilibrium, while remaining inert to the isobutylene. It is well known in the art that certain olefins, particularly isobutylene, polymerize very readily to form high molecular weight hydrocarbons. Heretofore, it has been difficult to convert butene-1 into butene-2 in the presence of isobutylene without causing polymerization of the isobutylene. Except for di-isobutylene, the polymers of isobutylene are of very little economic utility, while isobutylene itself is valuable as, for example, a feed stock for use in isoparaffin-olefin alkylation operations. It is therefore undesirable to polymerize the isobutylene during an operation to isomerize the butene-1 to provide butene-2.
Because of the relative lack of success in using previously known catalysts to provide a stable isomerization operation while remaining active and selective at temperatures favorable to high olefin conversion rates, previous attempts to provide an olefin double bond isomerization process have generally not been completely successful. The process of the present invention overcomes selectivity and stability difficulties and provides a practical and desirable method for shifting the double bond in olefinic hydrocarbons.